Diffuse phase transition in a surface quartz layer with variations in temperature

The temperature dependence of the α-phase concentration in surface layers of a solution-grown quartz crystal has been studied in the range 290–820 K. This has been achieved by measuring the intensity of the 695.1, 785.0, and 1061.5 cm^?1 bands in the ?″(ν) IR damping spectra. It has been found that, in a surface layer ～0.15 μm thick, the concentration of the α-phase behaves with increasing temperature as expected for a first-order phase transition, namely, before 800 K, it remains constant, after which at T → 846 K, tends to zero. At a distance from ～1 to 20 μm from the surface, however, the concentration of the α-phase starts to decrease already at ～350 K, while at 812 K it decreases to one-fifth of the original value. This is paralleled by an increase in the intensity of the 804 cm^?1 band assigned to the β-phase. The diffusive pattern of the α-β phase transition is initiated by distortion of the quartz crystal lattice around growth dislocations. The internal stresses arising in these layers have been estimated from the shift of the band maxima. It has been established that at distances up to ～1 μm from the surface, tensile stresses reaching ～300–400 MPa appear at 400 K. These stresses drive in the surface layer of the macrocrystal microcracks culminating in total destruction of the sample. The appearance of tensile stresses is assigned to an increase in volume of the macrocrystal layer located at a distance from ～1 to 20 μm from the surface and the growth in it of the β-phase concentration. At the same time, compressive stresses develop in a layer ～1 to 20 μm thick at a temperature above 500 K, which reach a maximum at ～650 K, to fall off thereafter with increasing temperature. The compression is caused by vibrations of growth dislocation loops in the temperature range specified.     

The influence of the structure of a nanocrystalline solid (sandstone) on the dynamics of microcrack accumulation on friction

On friction of a heterogeneous material: sandstone, flashes of triboluminescence are observed. Triboluminescence arises on the relaxation of excitation of free radicals ≡Si–O^–. These radicals form on disruptions of Si–O–Si bonds and are located at microcrack edges. Microcracks form at the boundaries of feldspar and quartz microcrystals. Their sizes range from ~0.4 to ~7 μm. The microcrack formation on friction leads to the spalling of feldspar and quartz microcrystals from a sample.     

Influence of a plasma jet on different types of tungsten

The influence of a plasma producing nonstationary thermal loads akin to edge-localized modes in a tokamak on different types of tungsten is investigated. Tungsten is irradiated by a jet of a hydrogen plasma generated in a plasma gun. The plasma density and velocity are on the order of 10²² m^?3 and 100–200 km/s, respectively, and the irradiation time is 10 μs. Two plasma flux densities, 0.70 and 0.25 MJ/m², are used. Structural modifications in irradiated single-crystal and hot-rolled tungsten samples, as well as in V-MP and ITER_D_2EDZJ4 tungsten powders, are examined. It is found that the plasma generates a regular crack network with a period of about 1 mm on the surface of the single-crystal, hot-rolled, and V-MP powder samples, while the surface of the ITER_D_2EDZJ4 powder is more cracking-resistant. The depth of the molten layer equals 1–3 μm, and the extension of intense thermal action is 15–20 μm. The material acquires a distinct regular structure with a typical grain size of less than 1 μm. X-ray diffraction analysis shows that irradiation changes the crystal lattice parameters because of the melting and crystallization of the surface layer. The examination of the V_MP tungsten powder after cyclic irradiation by a plasma with different energy densities shows that high-energy-density irradiation causes the most significant surface damage, whereas low-energy-density irradiation generates defects that are small in size even if the number of cycles is large.     

Mass ejection from shock-loaded free surfaces of steel

Abstract

The mass ejection from shock-loaded free surfaces of steel specimens under several condition of machining were measured using the piezoelectric quartz crystal gauge technique. At shock pressure of 45 GPa, the ejected mass quantities of steel with respect to the surface smooth finishes 0.4 μm (machinework) and 0.11 μm (vibration- roll compression) are 0.2 g/m² and 0.15 g/m², respectively. The ejected mass quantities of steel with respect to the surface smooth finishes 0.2 μm (polishing) and 0.1 μm (abrasiveness) are very small. Experiments show that the mass ejection is dependent on conditions of free surfaces. Surfaces defects, such as pits, scratches and machine marks are thought to be the primary reason for mass ejection.     

石英微透镜阵列的制作研究

叙述了采用氩离子束刻蚀的方法制作线列长方形拱面石英微透镜阵列.所制单元石英微透镜底部的外形尺寸为(300×106)um²,平均冠高7.07μm,平均曲率半径202.19μm,平均焦距404.38μm,平均F₂数为3.82,平均光焦度2.47×10³屈光度,扫描电子显微镜和表面探针测试表明,所制线列石英微透镜阵列的图形整齐均匀,单元长方形拱面石英微透镜的轮廓清晰,表面光滑平整.所制微透镜阵列用于高T_c超导红外探测器阵列的实验证实,微透镜的引入可以显著改善超导探测器的光响应特性.     

Microstructure and phase composition of a zirconium coating-silicon substrate system treated using high-current electron beams

The results of structural-phase conversions in a zirconium coating-silicon substrate system treated with low-energy high-current electron beams (LHEBs) are presented. It is revealed that the action of LHEBs with energy densities of 8–10 J/cm² leads to the formation of a eutectic layer containing clusters with a characteristic size of 40–50 nm (the melt of ZrSi₂ and silicon) at the zirconium-silicon interface. After the energy density reaches 12 J/cm², silicon dendrites and regions of silicide crystallites are formed in the surface layer 20–30 μm thick. Data on the characteristic sizes of dendrites and eutectic clusters have made it possible to perform numerical estimation of the surface-melt overcooling (12–25 K), the temperature gradients (3.7 × 10⁷?1.6 × 10⁸ K/m), and the interphase boundary velocity (0.8?3.2 × 10^?4 m/s).     

Rearrangement of the Ultrasmooth Surface of La3Ga5SiO14 Crystals at Heating

The morphology and phase composition of the surface of La₃Ga₅SiO₁₄ (langasite) crystals at annealing in a temperature range 1000–1200°C have been studied using electron and atomic force microscopy. It has been shown that trigonal lanthanum oxide (La₂O₃) crystals with sizes to 3–4 μm, as well as a microstructure with sizes to 50 μm with gallium excess, with the approximate composition of 15 mol % La₂O₃, 65 mol % Ga₂O₃, and 20 mol % SiO₂ are formed on the surface of langasite crystals annealed in air at temperatures above 1100°C. Possible reasons for thermal destruction of the compound can be a significant rearrangement of the disordered crystal structure of langasite caused by the interaction with air oxygen and under the intense surface diffusion of atoms of the crystal, as well as the incongruent character of melting of the La₃Ga₅SiO₁₄ compound. The revealed thermal destruction of the surface of langasite crystals should be taken into account when using this material to fabricate piezoelectric elements for operation at high temperatures.

     

Intense formation of intermetallic phases during implantation of aluminum ions in titanium

The results from microstructure and phase composition investigations of titanium in different structural states (with average grain sizes of 0.3 μm, 1.5 μm, and 17 μm) are presented following Al ion implantation using the Mevva-V.RU source (irradiating dose, 10¹⁸ ion/cm²). The implanted multiphase layers are found to form on the base of α-Ti grains. The size, shape, and localization of the formed phases (TiO₂, Ti₂O, TiC, Ti₃Al, Al₃Ti) depend strongly on the grain size of titanium target. It is shown that the nanostructural particles of TiO₂ phase are located mainly on dislocations in the body of target grains. A Ti₂O surface layer is found to arise in titanium with a grain size of 17 μm. It is established that an ordered Ti₃Al phase is located at a depth of more than 200 nm in the implanted layer along the bounaries of the titanium grains.     

Investigation of 4H-SiC epitaxial layers implanted by Al ions

4H-SiC epitaxial layers 26 μm thick with N _d ?N _a = 1 × 10¹⁵ cm^?3 grown by the CVD method on 4H-SiC commercial wafers were implanted by Al ions with energy of 100 keV and a dose of 5 × 10¹⁶ cm^?2. To produce the p ⁺?n junction, a rapid thermal annealing for 15 s at 1700°C was used. The obtained samples were studied by the local cathodoluminescence, X-ray diffractometry, and transmission electron microscopy. It was established that under specified conditions of implantation, the width of a region with a high content of radiation defects exceeded by two orders of magnitude, the depth of the projective range of Al ions and was equal to 40 μm. This result is explained by the combined contribution of the radiation enhanced defect diffusion and long-range action effect. A short-term high-temperature annealing resulted in the recrystallization of the specimen surface layer and enhancement of CVD layer structure.     

The influence of low-temperature silver-ion exchange on the spectral-luminescent properties of fluorophosphate glasses doped with PbSe

Changes in the absorption and luminescence spectra of fluorophosphate glasses doped with PbSe caused by low-temperature Ag⁺–Na⁺ ion exchange are considered. It is found that the silver distribution gradient in a near-surface layer about 16 μm thick leads to two different processes of interaction between metal and semiconductor nanoparticles. PbSe molecular clusters and quantum dots more efficiently grow in deep layers with a low silver concentration. The near-surface glass layers with a high silver concentration exhibit formation of Ag metal nanoparticles, on the surface of which interaction with PbSe molecular clusters leads to the formation of Ag–Se–Pb bonds, which transform into Ag₂Se layers in the process of heat treatment. The appearance of the new phase is confirmed by X-ray diffraction.     

A poly-Si thin film transistor fabricated by new excimer laser recrystallization employing floating active structure

We fabricated a high-performance polycrystalline silicon (poly-Si) thin film transistor (TFT) by new excimer laser annealing (ELA) method employing floating active structure. The new simple ELA method produces large lateral grains exceeding 4 μm. A novel poly-Si TFT that exhibits very high mobility (μ_FE=331 cm²/V s) and low leakage current has been successfully fabricated by single laser irradiation on selectively floating a-Si layer. Uniform lateral grains have been obtained with wide ELA process window.     

Analysis of the R0A product in n+-p Hg1−xCdxTe photodiodes

The influence of different junction current components (diffusion current for radiative and Auger 7 recombination mechanisms, tunneling and depletion layer currents) on the R₀A product of n⁺-p -Hg_1−xCd_xTe photodiodes is considered. The considerations are carried out for the 77–300 K temperature region and 1–15 μm cutoff wavelength. Optimum doping concentrations in the p-type region of n⁺-p abrupt junctions are determined, taking into account the influence of the tunneling current and of a fixed surface charge density of the junction passivation layer. Results of calculations are compared with experimental data reported by many authors. An attempt is made to explain the discrepancy between theoretical calculations and experimental data.     

Investigations on the effect of argon ion bombardment on the structural and optical properties of crystalline gallium antimonide

The effects of bombardment of 250 keV argon ions in n-type GaSb at fluences 2×10¹⁵ and 5×10¹⁵ ions cm^?2 were investigated by high-resolution X-ray diffraction (HRXRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). HRXRD studies revealed the presence of radiation-damaged layer (strained) peak in addition to the substrate peak. The variation in the lattice constant indicates the strain in the bombarded region. The out-of-plane (?_⊥) and in-plane strains (?_|) determined from the profiles of several symmetric and asymmetric Bragg reflections, respectively, were found to change with the ion fluence. Simulations of XRD patterns using dynamical theory of X-ray scattering (single-layer model) for the damaged layer yielded good fits to the recorded profiles. FTIR transmission studies showed that the optical density (α·d) of GaSb bombarded with different fluences increases near the band edge with increase in ion fluence, indicating the increase in the defect concentration. The density of the defects in the samples bombarded with different fluences was in the range of 3.20×10²¹–3.80×10²¹ cm^?3. The tailing energy estimated from the transmission spectra was found to change from 12.0 to 58.0 meV with increasing ion fluences, indicating the decrease of crystallinity at higher fluences. SEM micrographs showed the swelling of the bombarded surface of about 0.33 μm for the fluence of 2×10¹⁵ ions cm^?2, which increased to 0.57 μm for the fluence of 5×10¹⁵ ions cm^?2.     

Transformation of the Surface Structure of Marble under the Action of a Shock Wave

The structure of marble fracture fragments formed after the destruction under the action of a shock wave have been analyzed by Raman, infrared, and luminescence spectroscopic techniques. It has been found that calcite I in the surface layer of fragments with thicknesses of about 2 μm is transformed into high-pressure phase calcite III. At the same time, concentrations of Mn²⁺, Eu³⁺, and other ions decrease to about onefourth of their initial values.     

Properties of Hg implanted Hg1−x Cd x Te infrared detectors

Experimental performance parameters of Hg implanted Hg_1?x Cd _x Te photovoltaic detectors are analyzed. At 77K, for 8–14 μm band, a comparison is made between performances and theoretical ultimate diffusion limits in low frequency direct detection. Experimental features are well-explained by a model based on the Auger band-to-band process for carrier recombination. Peak detectivities exceeding 10¹¹ cm Hz^1/2W^?1, external quantum efficiencies as high as 90%, and zero-bias resistance-area products better than 1 Ω·cm² have been achieved in devices with 12 μm cutoff wavelengths. In the 3–5 μm band performances are far from the diffusion limit. Notwithstanding, at 77K zero-bias resistance-area products are better than 10⁴Ω·cm² and detectivities of the order of 10¹² cm Hz^1/2W^?1 were observed at 5 μm. Predominant generation-recombination contribution are present at room temperature in 1–1.3 μm photodiodes whose detectivities, primarily limited by the Johnson noise, at 1.3 μm are higher than 10¹¹ cm Hz^1/2W^?1 at 300 K. The high frequency response of the photodiodes is also discussed. Response times as low as 0.5 ns are reached despite some limitations arising from the implanted layer sheet resistance.     

Surface microstructure and morphology study of thin films produced from volatile fluorine-containing rare-earth β-diketonate complexes and their adducts

We present the results of a surface microstructure and morphology study of thin films produced from volatile fluorine-containing rare-earth β-diketonate complexes and their adducts. Films 0.2–0.4 μm in thickness were synthesized in vacuum by means of thermal deposition of the parent substances at a pressure of 5 × 10^?4?1 × 10^?3 Pa and a deposition rate of 3 × 10^?3 μm s^?1 (for NaNd(FOD)₄ films, the deposition rate was 8 × 10^?2 μm s^?1). The microstructure of films depends on the deposition conditions. The films of [NaNd(PTFA)₄] and [NaNd(FOD)₄] complexes and Ln(PTFA)₃ · S₁ adducts have an amorphous structure. The [NaNd(PTFA)₄(Phen)] and Nd(PTFA)₃ · S₂ films are characterized by a more ordered polycrystalline structure with the grain size ranging from 0.2 to 1.5 μm.     

Electron microscopy investigation of AlMg6 aluminum alloy surface defects caused by microorganisms extracted in space stations

The surfaces of AMg6 (aluminum-magnesium) alloy samples that have passed accelerated biocorrosion tests have been investigated in a Quanta-3D scanning electron microscope. The alloy samples have been treated with the Ulocladium botrytis Preuss fungus, which is an active destructive fungus and was previously extracted on surfaces of the International Space Station. Biocorrosion pits 2–10 μm in diameter, cavities the depths of which can reach 70–250 μm depth, and spots of modified color are found to be the most typical defects. The surfaces of large cavities consist of faceted cubic particles that are formed when the acid products of fungus metabolism interact with the alloy surface. The particles have an average size of 30 μm, which is close to the size of alloy grains. The microstructure of a biocorrosion layer has been investigated in a Quanta-3D microscope with the use of a focused Ga⁺ ion beam. The samples of 12-μm-wide transverse slices are obtained near large cavities and investigated in a Tecnai G₂₃0ST transmission electron microscope. The X-ray microanalysis of the defective layer has revealed the high concentration of oxygen in this layer. Obtained images indicate that the corrosion cavity surface has a complex porous structure.     

Variation in the structure of the surface layer of a heterogeneous solid (gneiss) on a shear

The structure of surface layers with a thickness of ~1 μm formed at destruction of gneiss is studied by means of photoluminescent and infrared spectroscopy. It is found that, in this layer, feldspar (plagioclase and microcline) crystals are completely destroyed and replaced by montmorillonite.     

Photoluminescence of implantation-induced defects in SiO2:Pb+ glasses

The luminescence of quartz glass with implanted Pb⁺ ions is investigated by time-resolved photoluminescence spectroscopy under synchrotron excitation. It is established that the glass layer modified with ions represents a microheterogeneous medium with a variable content of implanted ions predominantly in the form of Pb²⁺. Three different types of emission centers are detected that are created by radiation-induced defects of the SiO₂ matrix and localized electronic states of the amorphous lead-silicate phase.     

Physicomechanical properties of the surface of a zirconium alloy modified by a pulsed ion beam

The physicomechanical properties of the surface of the Zr-1% Nb zirconium alloy modified by a pulsed carbon ion beam with a pulse duration of 80 ns, an energy of 200 keV, and a current density of 120 A/cm² are studied at four regimes having different numbers of pulses. Irradiation by a carbon ion beam results in hardening of the surface layer to a depth of 2 μm, grain refinement to 0.15–0.8 μm, zirconium carbide formation, and a decrease in the hydrogen permeability of the zirconium alloy.